670 PHILOSOPHICAL TKANSACTIONS. [aNNO 1775. 



septa to the other. They appear to be so close as even to touch. In an inch in 

 length there are about 240, which multiplies the surface in the whole to a vast 

 extent. 



Of the Nerves. — The nerves in this animal may be divided into 2 kinds ; the 

 1st, appropriated to the general purposes of life ; the 2d, for the management 

 of this peculiar function, and very probably for its existence. They arise in 

 general from the brain and medulla spinalis, as in other fish ; but those from the 

 medulla are much larger than in fish of equal size, and larger than is necessary 

 for the common operations of life. The nerve which arises from the brain, and 

 passes down the whole length of the animal (which I believe exists in all fish) is 

 larger in this than in others of the same size, and passes nearer the spine. In 

 the common eel it runs in the muscles of the back, about midway between the 

 skin and spine. In the cod it passes immediately under the skin. From its 

 being larger in this fish than in others of the same size, one might suspect, that 

 it was intended for supplying the organ in some degree ; but this seems not to 

 be the case, as I was not able to trace any nerves going from it to join those from 

 the medulla spinalis, which run to the organ. This nerve is as singular an ap- 

 pearance as any in this class of animals ; for surely it must appear extraordinary, 

 that a nerve should arise from the brain to be lost in common parts, while there 

 is a medulla spinalis giving nerves to the same parts. It must still remain one of 

 the inexplicable circumstances of the nervous system. The organ is supplied 

 with nerves from the medulla spinalis from which they come out in pairs between 

 all the vertebrae of the spine. In their passage from the spine they give nerves 

 to the muscles of the back, &c. They bend forwards and outwards on the 

 spine, between it and the muscles, and send out small nerves to the external 

 surface, which join the skin near to the lateral lines. These ramify on the skin, 

 but are principally bent forwards between it and the organ, into which they 

 send small branches as they pass along. They seem to be lost in these 2 parts. 

 The trunks get upon the air-bladder, or rather di[) between it and the muscles of 

 the back, and continuing their course forwards on that bag, they dip in between 

 it and the organ, where they divide into smaller branches , they then get upon 

 the middle partition, on which they continue to divide into still smaller branches ; 

 after which they pass on, and get upon the small bones and muscles, which are 

 the bases for the under fin, and at last they are lost on that fin. After having 

 got between the organ and the abovementioned parts, they are constantly sending 

 small nerves into the organs ; first into the great organ, and then into the small 

 one; also into the muscles of the fin, and at last into the fin itself. These 

 branches, which are sent into the organ as the trunk passes along, are so small, 

 that I could not trace their ramifications in the organs. In this fish, as well as 

 in the torpedo, the nerves which supply the organ are much larger than those 



